The present invention relates to a method for the stabilization of a sex pheromone compound of pest insects, which is a higher aliphatic con, pound having at least one double bond in a molecule, used for the purpose of elimination of the pest insect by the method of mating disruption between different sexes of the insect species.
One of the serious problems in the agricultural technology against pest insects of agricultural plants in recent years is that, as a consequence of the use of various kinds of agricultural chemicals such as insecticides over many years heretofore, many species of pest insects have acquired resistance against insecticides along with adverse influences of agricultural chemicals not only against the agricultural workers' health but also against the health of the consumers of the agricultural products due to the residual trace amounts of agricultural chemicals therein.
Accordingly, a biological method is now under way of development which utilizes the sex pheromone emitted by the females of the pest insect to attract males of the same species. Namely, the chemical compound of the sex pheromone is chemically synthesized and distributed over the agricultural fields so as to effect disruption of the intersexual communication for mating by means of the sex pheromone resulting in a decreased efficiency of reproduction.
In this method utilizing sex pheromones for the elimination of pest insects, it is essential that the concentration of the sex pheromone compound in the atmospheric air is kept at a controlled level over a period of, for example, several months so that it is usual to prepare and use sustained-release pheromone dispensers containing the sex pheromone compound which is sustainedly released therefrom as is disclosed in Japanese Patent Publication No. 61-16361. Since many of the sex pheromone compounds of the pest insects belonging to the order of Lepidoptera are each a higher aliphatic compound having, for example, 8 to 30 carbon atoms and at least one double bond in a molecule, a serious problem to be solved in the utilization of pheromone dispensers is that the sex pheromone compound is highly susceptible to denaturation or degradation by the reactions of oxidation, isomerization, polymerization and the like at the double bond within a relatively short period of time when the dispensers are kept under outdoor conditions in the agricultural field. This problem is particularly difficult when the sex pheromone compound has a conjugation of double bonds or double bonds of the 1,4-pentadiene type or when it is a higher aliphatic aldehyde compound so that the method of utilization of pheromone dispensers cannot be practically used without solving this problem.
Various attempts and proposals have been made accordingly with an object to stabilize these sex pheromone compounds by the admixture of an antioxidant or ultraviolet absorber with the sex pheromone compound contained in the dispensers. For example, a proposal is made in Journal of Chemical Ecology, volume 14, No. 8, page 1569 (1988) for the use of butyl hydroxytoluene or butyl hydroxyanisole as an antioxidant of sex pheromone compounds and the antioxidation effect thereby can be further enhanced reportedly by the combined use of an ultraviolet absorber such as 2-hydroxy-4-methoxy benzophenone. In fact, the combined use of a specific antioxidant and a specific ultraviolet absorber has a synergistic effect to exhibit good stabilization of several sex pheromone compounds having unsaturation as compared with the single use of either one of these compounds. However, it is quite unclear what particular combinations of an antioxidant compound and an ultraviolet absorbing compound are the most effective for a particular sex pheromone compound.
A proposal is made in Japanese Patent Kokai No. 4-164004 for the combined use of an antioxidant of the hydroquinone type and a benzotriazole compound having a specific substituent group in the molecule as an ultraviolet absorber in order to obtain a high synergistic effect on the stabilization of an unsaturated higher aliphatic compound. While the effect obtained by the combined use of the benzotriazole compound may largely depends on the types and position of the side chain groups to the main chain of the compound, however, nothing is clear on the chemical structure which the benzotriazole compound should have in order to exhibit the highest synergistic effect. Further, Japanese Patent Kokai No. 4-178308 discloses a method for the stabilization of a sex pheromone compound by the combined admixture of an antioxidant and 2-(2'-hydroxy-5'-methylphenyl) benzotriazole and U.S. Pat. No. 4,568,771 discloses admixture of a sex pheromone compound with a benzotriazole compound such as 2-(2'-hydroxy-5'-methylphenyl) benzotriazole.